The present invention relates to a process and apparatus for fixing the position of a moving vehicle, whose direction of movement is known, on a map giving the distribution of a physical parameter measurable from the moving vehicle in a region surrounding a nominal or preestablished path of the moving vehicle. It is intended to solve the numerous navigational and guidance problems which occur for guiding moving bodies along a theoretical path to which they must be brought back in case of deviation.
Navigational processes and apparatuses of this type are already known, using terrain matching ("Aviation Week and Space Technology", Feb. 25, 1974, pp. 48-51; IEEE Transactions on Aerospace and Electronic Systems Vol. AES-15, No. 4, July 1979, pp. 547-554). Most are complex or require prestoring and measuring a number of parameter values.
It is an object of the invention to provide a process and apparatus using a simple procedure and requiring measurement of one parameter only, of relatively low cost.
According to the invention, a map is prepared which has two complementary parts in which the transparencies at each point, i and i, are in direction relation with and in inverse relation with the value of a predetermined parameter at this point relatively; during flight of the vehicle, the successive values of the parameter measured from the moving body are stored over a line of length l; the total light which pass through bands of said map parallel to the theoretical path and at a variable distance therefrom when there is directed across one of the two parts light of an intensity (flux) which, is directly related to the measured and stored parameter and across the other of the two parts light an intensity (flux) is inversely related to the two parts light an intensity (flux) this parameter, for several relative longitudinal positions along the line and the map, and the transverse and longitudinal position of the line is determined for which a correlation factor obtained from the measurement of the light fluxes is optimum.
The invention uses the fact that, in many cases, the direction of the course followed by a moving body whose position is to be fixed on a map is known, the differences with respect to the theoretical position corresponding simply to lateral offsets. By way of example, a problem which is easily solved using the invention consists of establishing the actual position of a manned or unmanned aircraft along its theoretical route and perpendicularly thereto, the parameter then being the height above the ground; another use is establishing the position of a boat, aircraft or missile along its set route and transversely thereto, using a magnetic field map. Then accurate measurement of the value and possibly direction of the local magnetic field is required.
Electrooptical correlator systems for providing an indication as to the degree of cross-correlation function between two signals are known (U.S. Pat. No. 3,283,133); however, there is no indication of the use of complementary reference documents, particularly maps, designed for navigational purpose.
According to another aspect of the invention, a navigation apparatus comprises means for receiving a two-part map providing a representative of a strip of ground on each side of a nominal path, one of the parts having at each point a transparency which is an increasing function of the value of a parameter at the point and the other a transparency which is a decreasing function of the parameter; lighting means are placed on one side of the map and direct, over a fraction of given length thereof, a light flux which, for the fraction on one part and for each longitudinal position, is an increasing function of the stored value of the parameter measured from the moving body and which, for the fraction on the other part, is a decreasing function of said stored value; means are provided for measuring the light fluxes which pass through several bands parallel to the moving direction, at varying distances from the theoretical path; means shift the longitudinal position of the illuminated fraction of the map; and correlation means determine the transverse position and the longitudinal position of the band for which a predetermined function of the light fluxes received is maximum or minimum.